Reversing a vehicle while towing a trailer can be challenging for many drivers, particularly for drivers that drive with a trailer on an infrequent basis or with various types of trailers. Systems used to assist a driver with backing a trailer frequently measure or estimate the position of the trailer relative to the vehicle with a sensor that determines a hitch angle. Among uses of this detected or estimated hitch angle is the determination of the hitch angle relative to a jackknife angle of the trailer relative to the vehicle. In general, a jackknife angle represents the maximum angle at which a change in direction of the trailer relative to the vehicle can be made with a maximum steering input in either direction, while the vehicle is still reversing. If a vehicle is reversed in a jackknife condition, in which the hitch angle is greater than the jackknife angle, the trailer will approach the vehicle, which could lead to a collision therebetween. Accordingly, the accuracy and reliability of hitch angle detection or estimation relative to the jackknife angle can be critical to the operation of the backup assist system.